The invention relates to pressure fluid operated cylinders, and more particularly, relates to arrangements utilized for securing a cylinder head in a fixed position with respect to the cylinder bore.
In the United States, a widely used cylinder assembly is made up of a circular barrel having discrete heads secured at the opposite ends thereof. The heads have a square cross-section, and are secured together, with the cylindrical barrel held therebetween, by tie rods which extend through the corners of the square heads and therebetween.
These square head tie rod cylinders are suitable for either pneumatic or hydraulic use and are manufactured to meet National Fluid Power Association (N.F.P.A.) standard dimensions. For a given power stroke, the standard dimensions are measured, for example, from the end of one head to the end of the other head, or measured from the end of one head to the end of the piston rod. Since the square head tie rod cylinders are manufactured in accordance with N.F.P.A. standards, they can be interchangeably mounted in various applications, and thus, have achieved substantially more widespread customer acceptance than cylinders which cannot meet all the N.F.P.A. standards. Although these cylinders have achieved wide spread use, they are relatively expensive to manufacture and assemble, and have limited flexibility with respect to mounting.
Another example of a fluid pressure operated cylinder having a different arrangement for securing the heads is disclosed in Panigati, U.S. Pat. No. 3,605,553, issued Sept. 20, 1971. Panigati discloses a circular cylinder having end members or heads fixed within the ends of a circular cylinder by means of resilient snap rings which have peripheral projections which are inserted in slots cut into the cylinder wall. Circular cap members, which abut against the ends of the cylinder, are secured to the heads to prevent inward longitudinal movement of the heads. The snap rings are the only members which prevent outward longitudinal movement of the heads, since the cap members are not directly secured to the cylinders. The specific details of the snap ring arrangement are disclosed in an earlier U.S. Panigati Pat. No. 3,421,786.
A typical example of a commercially available cylinder which embodies features of the above referenced Panigati patents is manufactured by WAIRCOM, located in Milano, Italy. The cylinder heads used by WAIRCOM are made of plastic, such as an acetalic resin, and each has a steel annular mounting ring molded therein and which faces an end of the cylinder, which cylinder is also made of steel. This mounting ring abuts against the previously mentioned snap ring to prevent outward longitudinal movement of the head, while the end cap, which is secured to the head by screws extending into the mounting ring, prevents inward movement of the head. A typical example of such a cylinder, is a WAIRCOM Series E cylinder, Model No. AKNBGB97/2. Although the plastic heads and the piston arrangement of the WAIRCOM cylinder are believed to be superior in cost and performance over the corresponding components in the square head tie rod cylinders previously discussed, the WAIRCOM cylinders do not meet all the N.F.P.A. standards, and thus, have achieved only limited use in the U.S.
More particularly, in the current WAIRCOM arrangement, the outer face of each WAIRCOM head is spaced from the end cap or end of the cylinder, about 3/16 of an inch. This is an exemplary reason for the WAIRCOM cylinders not meeting N.F.P.A. standards, e.g., the dimension of the cylinder from end to piston end, is too long. In addition to not meeting N.F.P.A. standards, WAIRCOM cylinders also have significant mounting limitations, because they present only a thin cylindrical barrel, which is difficult to utilize for mounting. Also, it is believed the WAIRCOM snap ring and cylinder slot arrangement cannot be used with a material softer than steel, such as aluminum, because the aluminum forming the slots tends to flow or lose its shape when under stress during cylinder operation.
Still another example of a different cylinder assembly having a different arrangement for securing the heads is disclosed in Nunnemacher, U.S. Pat. No. 3,005,669, which patent is assigned to the assignee of this application. Nunnemacher discloses a cylinder assembly with an elongated barrel having a square cross-section and including a cylindrical bore extending therethrough to define four longitudinally extending corners spaced around the bore. The Nunnemacher arrangement includes discrete end members or heads which have a square shape. Unlike the square head tie rod cylinder previously discussed, however, the Nunnemacher heads are secured to the ends of the square barrel by screws which extend through the heads and into the corners of the barrel. Although the Nunnemacher square barrel provides substantial flexibility over the aforementioned cylindrical barrels with respect to mounting, when the heads are secured to the ends of the square barrel, the resulting cylinder assembly, for a given power stroke, is too long to be compatible with all the N.F.P.A. mounting dimension standards. Accordingly, the Nunnemacher square barrel cylinder has achieved only limited use as an original or replacement cylinder.
This invention is concerned with this general area, and has among its objects to provide a cylinder assembly which eliminates some or all of the above noted and other disadvantages of prior art cylinders.
More particularly, the invention has among its objects to provide a cylinder assembly including a square barrel and a unique arrangement utilized to secure the heads within the bore of the barrel so that the cylinder assembly is flexible with respect to mounting, and yet meets N.F.P.A. standards.
The invention also has among its objects to provide such a cylinder assembly which is economical to manufacture and assemble, and which is particularly suited for pneumatic pressure use.